A method for forming a bump on under bump metallurgy according to the present invention is provided. A bonding pad is first formed on the active surface of a wafer. Subsequently, a passivation layer is formed on the active surface of the wafer and exposes the bonding pad. An under bump metallurgy is formed on the bonding pad. A layer of film is formed on the passivation layer and overlays the under bump metallurgy. Afterward, the portion of the film on the under bump metallurgy is exposed to a UV light and the exposed portion of the film is removed to expose the under bump metallurgy. A solder paste is applied to the under bump metallurgy and the remaining film on the wafer is removed. Finally, the solder paste is reflowed to form a spherical bump.
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1. A method for forming a bump, comprising the steps of:
providing a wafer having an active surface and at least one bonding pad formed on the active surface;
forming a passivation layer on the active surface of the wafer and exposing the bonding pad;
forming an under bump metallurgy on the bonding pad;
forming a layer of film on the passivation layer to overlay the under bump metallurgy;
performing an exposure process on the film, subjecting a portion of the film directly above the under bump metallurgy to a first exposure;
removing the exposed portion of the film, exposing the under bump metallurgy and retaining an unexposed portion of the film;
applying a layer of solder paste to the under bump metallurgy;
removing the retained portion of the film from the wafer by a de-taping machine; and
performing a second reflow process to have the solder paste formed into a bump.
13. A method for forming a bump, comprising the steps of:
providing a wafer having an active surface and at least one bonding pad formed on the active surface;
forming a passivation layer on the active surface of the wafer and exposing the bonding pad;
forming an under bump metallurgy on the bonding pad;
forming a layer of film on the passivation layer, overlaying the under bump metallurgy;
performing an exposure process on the film so that a portion of the film directly above the under bump metallurgy is subjected to a first exposure;
removing the exposed portion of the film to expose the under bump metallurgy and retaining an unexposed remaining portion of the film;
applying a layer of solder paste to the under bump metallurgy;
performing a first reflow process on the wafer;
removing the remaining film from the wafer; and
performing a second reflow process to have the solder paste formed into a bump.
7. A method for forming a bump comprising the steps of:
providing a wafer having an active surface and at least one bonding pad formed on the active surface;
forming a passivation layer on the active surface of the wafer and exposing the bonding pad;
forming an under bump metallurgy on the bonding pad;
forming a film layer on the passivation layer overlaying the under bump metallurgy;
performing an exposure process on the film, subjecting a portion of the film, directly above the under bump metallurgy, to a first exposure;
removing the exposed portion of the film, exposing the under bump metallurgy and retaining an unexposed portion of the film as a remaining film;
applying a layer of solder paste to the under bump metallurgy;
performing a second exposure on the remaining film;
removing the remaining film from the wafer by a de-taping machine; and
performing a second reflow process forming the solder paste into a bump.
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This application claims the priority benefit of Taiwan Patent Application Serial Number 096131780 filed Aug. 28, 2007, the full disclosure of which is incorporated herein by reference.
1. Field of the Invention
The invention relates to a method for forming bumps and more particularly, to a method for forming bumps on under bump metallurgy by micro-bubble film.
2. Description of the Related Art
It is common that a chip is electrically connected to external circuitry by wire-bonding in the art. However, more room is required to accommodate the bonding wires and the working frequency of the chip is also limited. Therefore, to solve the above problems, the flip-chip bonding technology has been developed to replace the conventional wire-bonding technology.
The so-called flip-chip bonding technology is first to form under bump metallurgy (UBM) on a chip and metal bumps are then formed on the under bump metallurgy. The chip can be connected to a substrate by the metal bumps with a reflow process.
According to the above flip-chip bonding technology, the structure of a metal bump formed by the conventional technique is illustrated in
Referring to
Referring to
According to the above method of using a strong base solution to remove the remaining photoresist layer 50, the strong base solution not only is expensive but also corrodes the under bump metallurgy 24 and passivation layer 23.
Accordingly, there exists a need to provide a method for forming bumps to solve the above-mentioned problems.
It is an object of the present invention to provide a method for forming bumps, wherein the remaining micro-bubble film can be easily torn off with a de-taping machine. There is no need to use the convention strong base solution to remove the remaining micro-bubble film. This avoids the corrosion of the under bump metallurgy and passivation layer.
In order to achieve the above object, the method for forming bumps according to the present invention is to form a bonding pad on the active surface of a wafer. A passivation layer is then formed on the active surface of the wafer and exposes the bonding pad. Afterward, an under bump metallurgy is formed on the bonding pad. A layer of film is formed on the passivation layer and overlays the under bump metallurgy. A photomask is positioned above the film and a UV light is used to perform a selective exposure process on the film. As a result, the portion of the film right above the under bump metallurgy is exposed to the UV light and therefore chemically reacts with it. The portion of the film not right above the under bump metallurgy is not exposed to the UV light due to the shielding of the photomask. A developer is then used to remove the exposed portion of the film. Subsequently, a layer of solder paste is applied to the portion of the under bump metallurgy exposed from the film and the wafer is subjected to a first reflow process to preheat the solder paste. Next, the wafer is irradiated by the UV light again to have the remaining film on the wafer exposed to the UV light. A de-taping machine is then used to tear all the remaining film from the wafer. The wafer is subjected to a second reflow process to have the solder paste formed into a spherical metal bump.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
Referring to
Next, a layer of film 460, such as a micro-bubble film is formed on the active surface 422 of the wafer 420 to overlay the under bump metallurgy 450 (see
According to the method of the present invention, the film 460 can be easily torn off with a de-taping machine after being exposed to a UV light. Accordingly, there is no need to use the conventional strong base solution to remove the film 460. This can avoid the corrosion of the under bump metallurgy 450 and passivation layer 440.
Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
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